It will work anywhere, but have to know (discover by trying it) what gearing you need for yourself and the hills. Experiment by leaving your bike in one gear and going for a ride. That way you might start with a good gear ratio.

If it's hilly and you need a low gear to get up the hills you give up some top speed on a flat surface. But if it's hilly you can coast down the hill anyway.

I have four single speed road bikes and one single speed trike to haul the dog in. The trike is geared very low so I can get up hills with a heavy load. But I don't mind losing top speed on the trike (most of the time). The lighter bikes can have much higher gearing and still go up hills so my speed on the flat is much better. A fast light bike makes it a little better, you can ride a higher gear.

It really depends on what you want from your riding experience. If you're looking for a way to discipline yourself to spin and build technique, a single speed will do nicely. Or, you can use your current bike and do what you've done... ride in just one gear. A fixie, however, is a very different ride experience. The fact that your legs are moving when the bike moves and moves faster or slower in direct relationship to your speed requires a whole different set of skills. You simply can't afford to lose focus on what you're doing. You learn to look ahead and anticipate things differently, because your legs will have to respond to differences in terrain; you can't coast and you can't switch to another gear. Additionally, there is something special about a drive train to which you have a very direct link. Some say it makes you feel more a part of the bike. Finally, there is a simplicity about a fixie that is hard to describe, but difficult to deny once you've tasted it. In some ways I think it's the most pure form of cycling there is. That's not to say it's better, just qualitatively different. For a newbie, it makes sense to see if you can try a friend's before investing. It also makes sense to have at least a front brake until you gain skills and experience with it. It's another niche in cycling that can enrich your overall riding. At the same time, there are those who never acquire a taste for it. No shame in that, but give it a shot. You might find it a nice addition to your current riding.

A singlespeed might be fun and simple for short trips and level ground. I think a fixed gear is designed to hurt you on the streets. It's like being tied to an engine. However, to each his own.

I converted an older bke to a singe speed,, I run a 46/16. here in texas it works quite well on the flats and the rolling hills. I use this basically just for winter rides as the rides are somewhat shorter do the colder weather. Occassionally in the summer I will ride it about 35 miles and it is a great work-out using one gear for the total ride. it is enjoyable but I do not think I would make a single speed or fixed gear my major riding bike.

No coaster brakes that way. :)

I haven't ridden single speed since my first bike about 52 years ago, but I used to frequently change from gears to fixed and back in my teens/early twnties. I would ride a 69" gear for general riding around and hills - even 25%, with a struggle - and 82" for time trials.

I recently, about a year ago, bought a Bianchi Pista and really enjoy riding it. For spinning I use 73" (48x18) and for pace line, 81" (48x16). I can cruise easily on the flat at 20mph and spin out at about 27-28mph in a sprint. The fixie is certainly a great way to build leg strength and to develop an efficient pedalling technique.

As for riding in traffic, which I don't do much of where I live, you just have to be a bit more predictive about stopping, but once you get used to it, it's OK. I use only a front brake. In a pace line I find it's easier on a fixie to adjust speed without braking. Just don't forget that you can't coast, especially when you are pushing hard or you might find that everything, including you might rotate:)